Now that the scientists and economists, using models, tree rings and ice cores, have completely eliminated the knowledge gaps about the past and present, they can move on to predicting the future. Onward!

In Florida, The three southeastern urban counties containing Miami, Fort Lauderdale, West Palm Beach) are aware of problems due to sea level rise, including costs to rebuild storm gates for drainage systems. A bit farther north, no one wants to notice that expensive waterfront houses are at risk, and the state government seems to ignore the issue.

Any global sea level rise is a big economic problem because most of the most valuable real estate is very near sea level. It's not really an ecological problem though, except to the extent that human development keeps ecosystems from moving inland. As I recall, sea levels were some 200 feet lower during the last ice age than they are today. The rise in sea levels since the end of the ice age has averaged somewhat less than 2 feet per century. Most of it happened early in the interglacial period, of course, but some has been ongoing as glaciers continue to melt and ocean temperatures continue to increase. Compared to 2 feet per century, the several inches projected by current climate models is not even out of line with the historical natural trend.

Yes, moving infrastructure will cost a lot of money, but it would have cost a lot of money anyway, without any anthropogenic global warming. All around the world, in almost every place that shows signs of long-term civilization, there are submerged cities and other archaeological sites attesting to the attractiveness and foolishness of building on the coast during an interglacial period. The only difference nowadays is the scale of development.

If only it were several inches that were predicted for 2100. Current estimates are in the range of 70 to 200 cm.
And post-glacial sea level rises were massive indeed, but over the past 8,000 years in which we built up our civilization sea levels were pretty stable. (See here for a graph.) We have never witnessed these 2 feet per century, at least not on a global scale.
Building on the coast during an interglacial would not have been that foolish in the absence of AGW. The 8,000 year stability might well have continued for another thousand years, and when the interglacial ends you'd expect the sea levels to fall, not rise. So I am not sure why you think we would have incurred the cost of moving coastal infrastructure anyway?

You largely make my point, which is that sea level rise is mostly an economic problem, not an environmental one.

On that last part, however, we would have incurred the cost eventually anyway unless we happen to just now be living conveniently at the very end of the current interglacial period. That seems unlikely, given that there is still a lot of ice at the poles and on mountains in between, but I'll defer to the paleoclimatologists for definitive evidence on that.

Your "current estimates" of sea level rise in the next century are quite a lot higher then I've seen, so I would like to know where you got them. The worst-case estimates I've seen were no more than one foot by 2100. 2-6 feet is clearly much more.

If we assume that AGW along will demand worldwide civil engineering to protect coastal cities against some known amount of sea level rise, then the obvious practical question is whether that protection would cost less, or more, than stopping the sea level rise. That in turn depends on a positive answer to the question "can we stop the sea level rise". If the answer is actually "no", then we're forced into the civil engineering solution anyway. Only if the answer is "yes" can we begin to compare costs. To do that properly we must also include the time value of money. Money spent today to cut CO2 emissions is more valuable than money spent 50 years from now to relocate buildings or raise highways.

You are right that until recently, the estimates were in the range of 18-59cm sea level rise by 2100 (IPCC, 2007). However, the IPCC cautiously did not factor in any melting of land ice because of high uncertainty in the rate at which that was happening.
However, sea level rises have tracked the upper confidence limits of earlier, similar IPCC predictions. http://www.skepticalscience.com/sea-level-rise-predictions.htm
Recent satellite data (GRACE project) have confirmed that land ice on Greenland and Antarctica are melting, and melting at an accelerating rate. See http://www.skepticalscience.com/GRACE-and-glaciers.html
New estimates that link observed temperature changes to observed sea level changes, in combination with predicted temperature changes due to CO2, give estimates of +0.7 to +2m by 2100.
We probably can't stop all of that rise, but certainly much or it. I agree that a good economic study would run a 'business as usual' scenario against scenarios with action to reduce greenhouse gas emissions - not against an bland assumption that no sea level rise will materialise.
But of course sea level rise is only one of the consequences of greenhouse gas emissions. A good study would take the whole gammut into account, including (positive and negative) changes in agriculture, fisheries, siltation, climate change, etc.

The envirowhackos first said the rise in sea levels would submerge Lady Liberty up to her neck in water. Last time i looked the estimate was more like a couple millimeters.

You realize of course a higher sea level would wipe out dozens of cities worldwide, which in and of itself is a virtue since cities are infested with "lets you and him conserve energy" hypocrites of the worst sort.

I have wondered how the estimates are arrived at. During some long lazy summers, I have made the following observation:

If you take a glass of water, put ice in it, and then fill it to a particular mark with water, the ice will extend above the mark on the glass.

If you let the ice melt, however, the water level will not rise, since the ice becomes more dense as it melts. Once it becomes water, by definition, its volume is equal to the volume of water it displaces.

So it seems to me that floating ice, such as is found in the arctic, should not raise the level of the oceans at all. Of course, ice that is perched atop land, such as in the antarctic or in Greenland, would still count.

I am by no means a climate scientist, but I wonder whether this observation has been taken into account. I would like to think it has been, but given the predisposition towards hyperbole in this area of discussion, I suspect that it has not.

The average temperature of all ocean water is 3.9 degrees celsius (most of which is very deep) the average surface temperature of the ocean in the summer is 15 degrees celsius. At that temperature, the density of water is 0.9992. It has expanded 0.08%. Considering it is summer on only half the planet at a time, the effect of expansion would even be smaller.

I think the 3.9 deg C is one of several guesstimates on average ocean temperature.

I'm not really sure what the posting on density is meant to show. Yes the density increase is small, but the important thing is the rate of sea level rise. Someone living on a costal delta isn't musch concerned as to the average density of seawater (which is about 1025 kg/m3, although it varies locally throughout the world. The Persian Gulf for example has a 1040 density which causes us some interesting problems due to the super high chloride content).

The great thing with global warming is: it will happen on both sides of the globe at the same time! Summer for all!

The average ocean depth is 3,790m. If you multiply that with 1 + 0.08% you get a sea level rise of 3m. Your temperature difference was 11C, so that's +30cm per degree Celsius. That would work out as +90cm by 2100 even if we assume 3C warming. That is not counting land ice melting. But it would materialise over a long time span, as it takes time to heat up the deep ocean.

I am surprised how many educated and articulate people simply dismiss the results of atmospheric physics, using quite emotional vocabulary usually reserved for religious quarrels. I suppose if they are sick, they happily use the medical science whose results have been reached exactly the same way, by observation, experiment and rational analysis.

Observation shows that global warming is a fact - anybody doubting it is welcome to my country and compare our glaciers now with ancient picture postcards.
The existence of the greenhouse effect of glass converting visible light to infrared is used by farmers every day, everywhere. That certain gases like CO2 and other gases have a similar effect is also experimentally proven beyond any rational doubt.
Finally it is also well proven that the percentage of CO2 in the atmosphere has been rising over the past decades; that is also plausible as everybody can see that indeed we are burning lots of stuff.

So theory predicts that, according to known facts, temperatures should rise; and they did. Sounds rather convincing to me.

For an intellectually honest person it is still possible to argue that other problems are more pressing and mankind's scarce resources should be used on those priorities (Lomborg and others said that). But to see smart people simply dismissing global warming as an invention of "them environmentalists" is incomprehensible to me.

The data for global warming is compelling. The data proving that it is due entirely to activities of man is less compelling, but the theory is sound. It stands to reason that 7 billion people are going to have a bigger impact on the planet's environment than 4 billion people. Just having that many people breathing is bound to increase CO2.

For argument's sake, assume you could use some Jedi mind trick on all the non-believers such that everyone is in total agreement regarding global warming.

So now what would you do?

Do we tell China and India and other developing nations that they must not develop? If we close a coal fired plant, what do we replace it with? Obviously the plant was built in the first place because society needed the electricity. How many rivers would you dam up? How much desert land would you cover over with solar panels? How many windmills would you erect? and where would you put them? How many nuclear power plants would you build? How much more would you be willing to pay for your electricity to reduce the effects of global warming? Double? Triple? Nothing? How are developing economies supposed to pay for it if western economies have trouble paying for it?

The problem with insuring against unlikely outcomes is that it is hard to trust estimates like this of economic activity decades in the future. This is particularly the case when environmentalists are so easily cast as millenialists, forever predicting catastrophic outcomes. The young couple invests in life insurance because a small fraction of young couples do actually die, leaving their children with no support. The scenario is unlikely, but credible. Environmentalist have been crying wolf on so many issues for so long that they have a huge credibility problem. And academics who espouse environmental causes have a similar problem: a few of their peers are such avid campaigners for one political outcome or another that they are prepared to shade the truth (or outright lie) to influence opinion. Every time an academic shows up on TV giving a passionate speech in favor of one action or another the whole profession loses. Academics are most convincing when they appear disinterested, aloof and mildly amused by the fate of the world. He should always understate his findings. A convincing academic gives the impression that the political battle raging around him is beneath his notice, because without objectivity his opinion is worthless. Passion will get you invited to environmentalist get-togethers, but it ruins the credibility of the profession.

It's a fine line between communicating results and recommendations for policy and advocacy. Scientists tried the dispassionate approach for decades, and largely have seen their messages ignored. One of the criticisms then was that scientists do not communicate enough with the public.

To me it is clear that scientists should do more than publishing papers in scientific journals and reports. Leaving the task of informing the general public to journalists and politicians made it easy for vested interests to influence public opinion by getting false experts to dismiss the science, and so prevent effective action being taken. I welcome it if scientists appear more in the public press to explain their findings and the implications for policy.

Lies are of course fatal to anyone's credibility. But you don't give an example of a scientist willingly and knowingly lying, and I strongly have the impression that most of the lying and deceit is on the other side, with those who dismiss the science.

It took several decades to get the scientific finding that tobacco kills translated into effective policies to reduce smoking. (And in many countries that still hasn't happened.) This cost the lives of tens of millions of people. We must do better with climate change.

Gleick did not lie about the science. He gave a false name to obtain documents attempting to demonstrate the aforementioned influence on public opinion by vested interests. And then he revealed what he had done, and apologized. Got anything else?

Prehaps the reason this kind of estimate does not have as much impact as it should is people think the cost will be shared equally, and we are more interested in our relative wealth than absolute ... okay to be part of a poor world so long as I don't lose my percentile position.

Estimating those who have most to lose - low lying US cities and anyone else with valueable beach front property subject to expensive local taxation for extra sea defences, etc should get a more passionate response.

why does such a large ammount of money be spent on resarching sea level change whrn it could be used to help countries get out of reccession?
After we are out of recession then we can focus on trivial matters such as sea level change. If you think that sea level will rise due to ice melting then that is not true, the ice is merely water help up in storage, all that water used to be in the planet so why worry about it being released, anyway the ice boundry has increased this year instead of decreasing.

Well, on land, part of that US $ 1.98 trillion loss is already evident in my neighborhood of Kariobangi South, Nairobi.
Over the last 10 years, due to increased dust and pollution propelled by faster winds lacking arboreal breaks, low grade pediatric pulmonary and gastro-intestinal infections have increased at least 3-fold.
Treatment costs, at about US $ 14 per bout, has thus increased by US $ 140,000 for the 5,000 local cases annually, an amount adequate to build and equip an 8-class primary school.
If each of the 6,000 homesteads spent US $ 5, in cash or kind to 4,800 the above amount would be saved.

Judging by the comments below, one would have to assume that the dialogue concerning Global Warming has reached the level of farce.
Since Economist readers tend to be highly educated, one must assume that the more intelligent a person is, the more skeptical they become about Climate Change alarmists like Gore, the UN and every climate scientist funded by every government in the world. The tide has turned.

I think the extreme reactions have a trace of fear about them…hence alarmists!!…kill the messenger!!. Certain industries, their dependent livelihoods are threatened and require drastic change.
Hence the fear of stepping out of comfort zones.
Unfortunately, in the transit into the information age, accompanied by an increased multi-dimensional model simulation capacity will show the rest of the world what we are experiencing in Africa.
We feel it on our skins as temperatures get higher, in our stomachs as unpredictable weather affects agricultural outputs, and our bodies as mosquitoes migrate to areas hitherto too cold for them.

Every intelligent person I know - doctors, lawyers, economists, accountants, scientists, bankers - accepts the science of climate change; maybe because they are intelligent they appreciate the onus of proof required of the peer-reviewed process.

If you step away from identity politics, ie outside of America, you will find that most intelligent people accept the science.

Mr. Seeker thinks that people like us troll the internet for Global Warming articles and then ridicule them. To him we are not TRUE Economist readers because we do not always agree with the articles they print. In his eyes we are too stupid to understand the truth that Global Warming will doom mankind. In reality, we are not too stupid to understand the economic ramifications of imposing huge taxes on us now to combat a dubious computer-model-based crisis that may occur 100 years in the future.

Mr. Gumby. (Is that really your name?!) you are being too harsh. This should be about science and economics not personal attacks. I have been guilty of that myself and I apologize. I like to make jokes about GW scientists in general, but there is too much of it going on in the real world. We have our beliefs, and when we feel that what we present as facts are having no effect on other's opinions, we resort to personal attack.
For me, it's just a bit of fun. For others, GW is deadly serious. And I respect that in them. Keep commenting, Sense Seeker. You are a most worthy opponent.

That's an unexpected compliment, Gwen. Thank you. And to clarify, I wouldn't deny anyone the pleasure of commenting on climate-related articles on this website. My own statistics are scarcely better than yours, in the past few years.

And in that, I find myself mirroring the tone of the postings I comment on. Serious discussion points invite serious responses. Opinions masquerading as facts invite sarcasm, false facts deserve ridicule. Personal attacks get a similar response. It's just too tempting - I like a good debate and sharp-witted responses (such as that of Edgar above).

But yes, I can only take climate change seriously. I have read quite a bit about the science, I know about how tobacco companies subverted the science and influenced public opinion to sell their deadly wares, and I see similar tactics employed in this debate. Hence the occasional grumpiness when I suspect people are not honest in what they write, or are not open to what I see as rational debate.

First things first. The "climate change is a myth" myth needs to be dispelled. There is a consensus among the scientific community that this is happening, and it would be the height of irresponsibility to ignore them.